In the fabrication of transducers, it is frequently necessary to join parts through the use of adhesive. An example of an application of such a transducer is a scale that utilizes a strain gauge for the purpose of measuring the deflection of a beam. The strain gauge must be attached to the beam in such a way that the deflection of the beam is accurately measured by the strain gauge. This requires that the strain gauge by firmly attached to the beam with a minimum of adhesive holding the strain gauge to the beam.
Prior art methods for curing adhesive for bonding a strain gauge to a beam involved applying adhesive to the strain gauge and attaching it to a beam and curing the adhesive. This was accomplished by mechanically clamping the strain gauge to the beam with the adhesive therebetween in a fixture and placing the fixture in a heating chamber which was then brought to the curing temperature of the adhesive. The quality of the transducer is materially affected by the bond line temperature, i.e. the temperature reached by the adhesive. Achieving the proper bond line temperature requires a considerable amount of time so that the temperature of the entire mass may be brought to the curing temperature relatively uniformly. In this scheme of curing, the entire fixture had to be heated.
As is known, it is difficult to control the temperature within a heating chamber, particularly when the heat is supplied by resistance heating. The heat from the atmosphere is transferred to the fixture and the bond line eventually reaches the desired temperature. The shortcoming of this method of curing the adhesive of a transducer is that furnaces, whether they be resistance furnaces or combustion furnaces, do not display either uniform increase in temperature or uniform temperature throughout the chamber. As a consequence, some of the transducers will achieve a proper curing of the adhesive while others will either by cured at too high or too low a temperature. The rate of heat rise also could be too high or too low. Furthermore, a large amount of energy is required in this mass method of curing for the small amount of material that is to be cured. A still further disadvantage is that only when a large number of transducers are being fabricated does the method approach any type of economic justification.